It is found that a high-frequency source (or multiple) imbedded in a moving patch of fluid emits a constant acoustic power independent of the motion. (The directivity is, however, altered). This holds when the wavelength λ ≪ radius R′ of the entire region of flow. At the other extreme λ ≫ 2πR′ it appears that the acoustic power is enhanced by the motion, somewhat (but not exactly) as the emission of a source is enhanced by motion through fluid at rest. A typical wavelength of a radiating eddy in a jet lies between the two extremes and a limited convective enhancement of the power is inferred. The amount should be less than that predicted by Light-bill or the much more conservative values suggested by the work of Ribner; it could conceivably lie within experimental error. justifying the nonconvective law, power ∼U8, found by measurement.
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H. S. Ribner (1960) studied this question.